Noble metal alloys

ABSTRACT

NOVEL GOLD ALLOYS HAVING DESIRABLE PROPERTIES OF HARDNESS AND SOLIDUS TEMPERATURE ARE PROVIDED WHICH COMPRISE ABOUT 67.0 TO 87.0 PERCENT GOLD, ABOUT 7.0 TO 15.0 PERCENT PALLADIUM, ABOUT 2.0 TO 10.0 PERCENT PLATINUM, ABOUT 0.5 TO 1.0 PERCENT OF IRON AND ABOUT 0.5 TO 2.0 PERCENT TIN, ALL BASED UPON THE TOTAL WEIGHT OF THE ALLOY. OPTIONAL ALLOYING ELEMENTS INCLUDE UP TO ABOUT 2.0 PERCENT SILVER, 1.5 PERCENT ZINC, 1.0 PERCENT INDIUM AND 1.0 PERCENT RHENIUM.

Uni ted States Patent 3,666,540 NOBLE METAL ALLOYS 7 Arthur PeterBurnett, Taritfville, Conn., assignor to The J. M. Ney Company,Bloomfield, Conn. No Drawing. Filed July 26, 1967, Ser. No. 656,048

Int. Cl. C22c /00; B32b /04 I US. Cl. 117-129 8 Claims ABSTRACT OF THEDISCLOSURE Novel gold alloys having desirable properties of hard- 7 Imess and solidus temperature are provided which comprise about 67.0 to87.0 percent gold, about 7.0 to 15.0 percent palladium, about 2.0 to10.0 percent platinum, about 0.5 to 1.0 percent of iron and about 0.5 to2.0 percent tin, all based upon the total weight of the alloy. Optionalalloy ing elements include up to about 2.0 percent silver, 1.5 percentzinc, 1.0 percent indium and 1.0 percent rhenium.

BACKGROUND OF THE INVENTION Gold-base alloys containing platinum,palladium and the combination thereof are commonly employed for variousapplications in dentistryand in industry. In dentistry, such alloys finda large amount of use as base structures upon which porcelains are firedto provide tooth structures, crowns and the like. In industry, suchalloys find widespread application in electronics applications becauseof their resistance to corrosion and desirable conductivity; onoccasion, ceramics are bonded thereto for insulating and other purposes.

Generally, the gold alloys intended for use in applications whereporcelains or other ceramics are to be fired in contact therewithrequire high solidus temperatures. Many other alloys which have beendeveloped for this purpose require constant-temperature age hardening orother highly critical hardening conditions in order to develop areasonably high degree of hardness. In addition,

" 3,666,540 Patent ed May 30, 1972 SUMMARY OF THE INVENTION 1 It has nowbeen found that foregoing and related objects can be readily attained inaccordance with-the present invention wherein a noble metal alloy isprovided comprising about 67.0 to 87.0 percent gold, about 7.0 to 15.0percentpalladium, about 2.0 to 10.0.percent platinum, about 0.5 to 1.0percent iron andrabout 0.5. to 2.0 percent tin, all based upon the totalweight of the alloy.

In addition, minor amounts of impnrities up to about 5.5 percent ofcompatible alloying elements may be present including up to about l.0percent rhenium, up to about 2.0percent silver, up to about 1.5 percentand up to about 1.0 percent indium. j

The alloys desirably contain small amounts of rh'enium to produce grainrefinement and a highly desirable when such alloys are used in the castcondition rather than in a wrought condition, variations inhardenability may be encountered with variations in casting temperature.

Typically, the gold-base alloys for ceramic applications will hardenonly to 15 kg. Brinell hardness levels on the order of 150 B.H.N. unlessa constant-temperature age hardening heat treatment is employed. Withage hardening at constant temperatures from a solution heat-treatedcondition, these alloys may reach a 15 kg. Brinell hardmess on the orderof about 170 B.H.N. Howeer, such alloys at the indicated hardness levelswill exhibit a maximum tensile strength on the order of about 50,000p.s.i. in the cast and age hardened condition.

Moreover, the gold-base alloys for the aforementioned applicationsgenerally have solidus temperatures below about 1150 centigrade whichlimit their use in conjunction with brazing alloys, and the temperaturesat which firing of the ceramic materials can be effected. In addition,the problem of thermal expansion generally dictates .6

equiaxedstructure. Silver, zinc and indium tend to promote fluidity ofthe alloy while zinc may provide some benefit from the standpoint ofhardness. In addition, these several optional alloying elements arebeneficial from the standpoint of facilitating predetermination of thecoefiicients of thermal linear expansion. Full hardness can be developedin this alloy by simple air cooling from temperatures above 980centigrade. Generally, cooling to about to 150 centigrade should be at arate of about 80 to centigrade per minute from a temperature above about980 centigrade. This air cooling is conveniently effected by dead aircooling wherein the alloy article is supported upon an insulating blockand shielded by a cover or the like to minimize convection. Constanttemperature age hardening may also be employed by heating the alloyarticles at a temperature ofabout 530 to 545 centigrade for fifteen tothirty minutes followed by air cooling. If cooling is effected toorapidly by quenching from about 980 centigrade, the alloy will be in anannealed condition in which cold working is readily accomplished. I I VThe alloys of the present invention vary from light yellow to white,depending upon the ultimate gold content so that they may be used forvarious applications where color is of significance. It has been foundthat these alloys are extremely useful for applications where 1porcelains or other ceramics are to be fired in surface con tacttherewith so as to provide a bonded structure. Porcelains and otherceramics which are fired at temperatures of 870 to 1070 centigrade maybe used readily with the alloys of the present invention to obtainhighly desirable composite structures since the cooling rate for thecomposite articles after firing of the ceramic may ideally fall withinthe preferred cooling rate for the alloy of the present invention todevelop optimum hardness. The nature of the hardening system of thepresent invention is not fully understood. It wouldappear that twomechanisms may be participating in generating the highly desirableresults obtained, the first being iron/platinum and the second beingiron/platinum/tin. It has been observed ,that the atomic ratio of ironto platinum must fall within the range of about 0.l0.6:1.0,andvpreferably in the range of about 0.40.6:1.0.

Generally, the solidus temperatures of the alloys of the presentinvention will be in excess of 1180 centigrade so as to permit not onlyfiring with a large variety of ceramic materials but also brazing andexposure to other operations involving relatively high temperatures. Thealloys have been noted to be relatively insensitive to castingtemperature in terms of ultimate hardness and to reliably develophardness levels in excess of 175 B.H.N. using a 15 kg. load. Byoptimizing the heat treatment of the alloy, hardness levels on the orderof 225 B.H.N. are readily attainable. The coefiicient of expansion isreadily predictable to two significant figures at temperatures in therange of 21 to 500 centigrade. Variations in the coefiicient of thermallinear expansion can be obtained from LElXIO- O- to'1.5 10- Cr in theabove range.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred alloys of thepresent invention have the following formulation:

Element: Percent by weight I Gold 78-85 Palladium 8-13 Platinum 4-8Iron' 0.7-1.0 Tin 0.9-1.4 Rhenium 0.07-0.2

, Illustrative of the efiicacy of the present invention are thefollowing specific examples wherein all parts and percentages are byweight unless otherwise indicated.

Examples 1-10 A series of gold base alloys were prepared and cast inphosphate-bound investment molds. In all instances, the castings wereslowly air cooled from 926 centigrade un- The alloys of Examples 1-5were cast at temperatures of 1315 to 1650 centigrade without evidence ofany degradation in hardenability from the as-cast condition. The alloyof Example 2 in the cast and age hardened condition was found to have anultimate tetnsile strength in excess of 90,000 psi. The several alloyswere found to have desirable castability and the castings were found tobe free from hot tears.

Exemplary of the higher solidus temperature of the alloys of the presentinvention are 1188 centigrade for the alloy of Example 2, ll73centigrade for the alloy of Example 4 and 1232 centigrade for the alloyof Example 5. Exemplary of the predictability of the coefiicient ofthermal linear expansion is the fact that the thermal coeflicient forthe alloy of Example 1 was predicted and experimentally determined as1.4x l C. and that of the alloy of Example 2 was similarly predicted andexperimentally determined as 1.4 Cr

Example 11 A feldspar porcelain without any binder was coated upon thesurface of a casting of the alloy of Example 2. Following firing at ,atemperature of 926 centigrade, the composite was placed on an insulatingblock and covered by a Pyrex breaker so as to minimize convectioncurrents.

4 The alloy of the resultant composite structure was found to have a 15kg. Brinell value of 180 B.H.N.

Thus, it can be seen that the present invention provides novel gold-basealloys with highly desirable casting 5 characteristics which aresusceptible to age hardening to high hardness levels during air cooling.The alloys of the present invention have advantageously high solidustemperatures and predictable coeflicients of thermal expansion which arehighly compatible with porcelains and other ceramics used in dentistry,electronics and other industrial applications. These alloys providecomposite structures with porcelains and other ceramics ofi eringsignificant utility in view of their hardness, corrosion resistance andconductivity. Moreover, the alloys of the present invention are usefulin other applications wherein relatively high heats are to beencountered such as brazing operations and the like.

Having thus described the invention, I claim:

1. A gold alloy consisting essentially of about 7.0 to

15.0 percent palladium, about 2.0 to 10.0 percent platinum, about 0.5 to1.0 percent iron about 0.5 to 2.0 per.-

cent in, 0.0 to 2.0 percent silver, 0.0 to 1.5 percent zinc,

to 13.0 percent, the platinum content is about 4.0 to 8.0

percent, the iron content is about 0.7 to 1.0 percent and the tincontent is about 0.9 to 1.4 percent. I

3. The alloy of claim 1 wherein the atomic ratio 0 iron to platinum isabout 0.4-0.6: 1.0.

4. The alloy of claim 1 wherein rhenium comprises 0.03 to 1.0 percent ofthe total weight of said alloy.

5. The alloy of claim 2 wherein the atomic ratio of iron to platinum isabout 0.4-0.6:l.0, and wherein nhenium comprises 033 to 1.0 percent ofthe total weight of said alloy.

6. A structure comprising an element formed from a gold alloy consistingessentially of about 7 to 15 percent palladium, about 2.0 to 10 percentplatinum, about 0.5 to 1 percent iron, about 0.5 to 2 percent tin, 0.0to 2.0 percent silver, 0.0 to 1.5 percent zinc, 0.0 to' 1 percentindium, 0.0 to 1.0 percent rhenium, and the balance gold, said goldbeing present in an amount of about 67 to 87 percent, all upon the totalweight of said alloy and a ceramic element bonded thereto formed byfiring against the surface of the alloy element a ceramic materialselected from the group consisting of porcelains, glass and enamels.

7. The structure of claim 6 wherein said alloy hasa gold content of 78to percent, a palladium content of 5 about 8 to 13 percent, a platinumcontent of about 4 to 8 percent, an iron content of about 0.7 to 1.0percent and a tin content of about 0.9 to 1.4 percent.

8. The structure of claim 6 wherein said alloy element has a 15 kg.Brinell value in excess of BHN.

